Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$54.77	8.492%	$59.4211	$59.42	$59.40	$59.40
Purchase #2	$170.82	7.545%	$183.7084	$183.71	$183.70	$183.70
Purchase #3	$46.73	12.841%	$52.7306	$52.73	$52.75	$52.70
Purchase #4	$92.43	11.443%	$103.0068	$103.01	$103.00	$103.00
Purchase #5	$61.59	13.697%	$70.026	$70.03	$70.05	$70.00
Purchase #6	$156.59	5.106%	$164.5855	$164.59	$164.60	$164.60
Purchase #7	$58.26	4.741%	$61.0221	$61.02	$61.00	$61.00
7 purchase totals =	$641.19		$694.5005	$694.51	$694.50	$694.40